1. Field of the Invention
The present invention relates to a method for generating negatively charged oxygen atoms in a vapor phase and an apparatus used therefor, more specifically to a method for generating negatively charged oxygen atoms, which has advantageous merits in maintaining food freshness, such as inhibiting strawberry mold and maintaining tuna freshness, and which are used for air cleaners etc. to utilize their favorable effect on the human body, and an apparatus used therefor.
2. Discussion of the Related Art
Negatively charged oxygen atoms (O.sup.- ; atomic oxygen radical anion) have been conventionally produced by attaching low-energy electrons to oxygen atoms generated by electric discharge, etc. However, this method has a problem in that high energy is necessary for maintaining a high vacuum and for electric discharge or an electron gun.
Recently, a new method for generating negatively charged oxygen atoms has been proposed, in which ozone is generated by electrically discharging in an oxygen gas, the resulting ozone is irradiated with ultraviolet rays, and low-energy electrons are attached to the resulting oxygen atoms to produce O.sup.- (Japanese Patent Laid-Open No. 62-237733). In this method, a generator is used, which comprises a vacuum chamber having a window capable of irradiating ultraviolet, an electric discharge unit, and a low-energy electron gun. However, this generator has a complicated structure and also requires higher energy for electric discharge and the electron gun. In addition, a high vacuum is required to achieve electric discharge, which results in extremely high running cost.
On the other hand, a method in which dinitrogen monoxide is introduced to a surface of a thermally or chemically reduced metal oxide to produce O.sup.- on the metal oxide has been conventionally known. Specifically, a metal oxide, for instance, titanium monoxide, zinc oxide, aluminum oxide, or magnesium oxide, is thermally or chemically reduced, followed by introduction of dinitrogen monoxide to the surface thereof, to generate O.sup.- through the process of N.sub.2 O.fwdarw.O.sup.- [Yuki Kagaku Gosei, Vol. 40, No. 8, (1982)].
In this method, however, the reaction site of a reaction substrate is limited to the metal oxide surface, because O.sup.- is generated thereon. For this reason, the reaction of O.sup.- with the reaction substrate depends on the oxidation state of the metal oxide, and in order to obtain the desired oxide, a metal oxide suitable for its purpose has to be selected. Also, this method has a problem in operation, because a dinitrogen monoxide gas is a toxic or laughing gas.